The present invention claims priority from Japanese Patent Applications No. 2000-014715 filed Jan. 24, 2000 and No. 2000-017324 filed Jan. 26, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a hybrid car using both an internal combustion engine and a motor-generator and, particularly, the present invention relates to a novel hybrid car capable of realizing a series-parallel hybrid system, which utilizes a single electric rotary machine and has small fuel consumption.
2. Description of Related Art
The hybrid car having an internal combustion engine and a motor-generator can be roughly classified to a series system and a parallel system on the basis of driving system.
In the hybrid car of the series system, an internal combustion engine is mechanically connected such that the internal combustion engine drives a generator and an axle of the car is mechanically connected such that the axle is driven by a motor. That is, the car is driven by the motor supplied with electric energy generated by the generator driven by the internal combustion engine. In the series system, it is usual that the electric energy supplied from the generator is used to recharge a storage battery and the motor is driven by the storage battery. When braking energy is regenerated in the series system, the motor ganged with the axle is switched to a generator mode and rotary energy supplied from the axle is converted into electric energy with which the storage battery is recharged. Fuel (gasoline, etc.) used in the internal combustion engine is externally supplied and the storage battery may be recharged by externally supplying recharging current thereto.
The parallel system is constructed by mechanically connecting a motor-generator directly to an internal combustion engine driving an axle. By using the motor-generator as a motor and supplying electric energy from a storage battery to the motor, it is possible to drive the axle by both the internal combustion engine and the motor. In braking the car, it is possible to perform a regenerative braking for recharging the storage battery by operating the motor-generator as a generator. Further, it is possible to recharge the storage battery with electric energy generated by the motor-generator during a parking time of the car by shifting a change gear to neutral or decoupling a clutch to switch the operating mode of the motor-generator to the generator mode, driving the motor-generator operating as the generator by the internal combustion engine and supplying an electric output of the motor-generator to the storage battery. Alternatively, it is possible to recharge the storage battery by operating the motor-generator as the generator during a running state of the car with the change gear and the clutch being connected and driving both the axle and the generator by the internal combustion engine. Fuel for the internal combustion engine is supplied externally and the storage battery can be recharged by supplying recharging current externally. This system has been utilized in HIMR""s manufactured and sold by the assignee of this application.
The series system allows a car to be operated by selectively setting the rotation speed of an internal combustion engine regardless of the running state of the car. That is, in the case where the recharging of the storage battery is performed during either the running state or the parking state of the car, it is possible, according to the load current and the recharging state of the storage battery, to control the operation of the internal combustion engine such that rotation speed thereof becomes in a range within which fuel efficiency is high or in a range within which the amount of exhaust gas becomes minimum.
On the contrary, since the parallel system can operate both the internal combustion engine and the motor, it is possible to increase the maximum torque generated in running on an uphill road or in starting with acceleration. However, since the rotation speed of internal combustion engine is generally changed correspondingly to the running condition of the car, it is impossible to continuously drive the car at rotation speed or speeds in the range in which fuel efficiency is high. Therefore, the parallel system is considered as to be suitable for a large size vehicle such as a bus or truck which requires a large instantaneous maximum torque.
A system which utilizes the merits of both the series system and the parallel system is disclosed in JP H11-75302 A filed by the present assignee. A construction of the system is shown in FIG. 1. In FIG. 1, a vehicle of the system uses first motor-generator 2a and second motor-generator 2b. First motor-generator 2a is directly connected to internal combustion engine 1 and first clutch 3a is provided between first motor-generator 2a and change gear 4. second motor-generator 2b is connected to the change gear side of first clutch 3a through second clutch 3b. Second motor-generator 2b is connected to a main shaft through gear train 4a provided on an input side of change gear 4.
In this construction, since, when first clutch 3a is separated, rotation of internal combustion engine 1 is not transmitted to change gear 4, internal combustion engine 1 drives first motor-generator 2a as a generator to recharge a storage battery and the vehicle is driven with energy supplied from second motor-generator 2b and the storage battery by operating second motor-generator 2b as a motor and connecting second clutch 3b. In this operation mode, the system becomes the series system mentioned above. Since, when first clutch 3a is connected in this operation mode, the vehicle can be driven directly by internal combustion engine 1 and first motor-generator 2a can be utilized as the motor simultaneously, this system becomes the parallel system mentioned above. When this system is operated as the series system, it is possible to selectively set an engine rotation in an efficient rotation speed range to thereby improve the fuel consumption and, when this system is operated as the parallel system, it is possible to increase the instantaneous torque. In the system shown in FIG. 1, when the regenerative braking is performed, it is possible to effectively regenerate braking energy from second motor-generator 2b by separating first clutch 3a, without influence of friction of internal combustion engine 1. However, it is necessary, in this system, to control the two clutches, as mentioned.
German Patent Publication No. 2943554 (Volkswagen) discloses a technique, which belongs to the above mentioned parallel system and in which an internal combustion engine, a motor-generator, a first clutch and a change gear are connected in the sequence and a second clutch is provided between the internal combustion engine and the motor-generator. That is, the disclosed construction allows a vehicle to be operated as either the parallel system or a modified series system with using a single electric rotary machine. In the disclosed system, however, it is necessary to provide the second clutch, which is large in size, and to operate the large clutch correspondingly to the operation mode. Therefore, a special clutch mechanism using an oil pressure system and an electronic device for controlling the clutch mechanism are indispensable.
Demand for hybrid car, particularly, hybrid cars having high fuel efficiency, is very brisk in the recent market. Further, there is a severe demand for hybrid car having high exhaust gas purification performance looking far ahead into the future. Under the circumstances, it becomes necessary to study the possibility of employment of the above mentioned series system in a large commercial vehicle such as a bus and/or truck. In the series system mentioned above, a vehicle can be driven by electric energy obtained from a generator driven an internal combustion engine, in which case, the rotation speed of the internal combustion engine is basically in no relation to the running speed of the vehicle. Therefore, it is possible, in the series system, that the internal combustion engine can utilize a rotation speed in a range preferable in view of the fuel consumption characteristics and the exhaust gas characteristics thereof.
In the series system, however, two electric rotary machines are required basically. Since the size of electric rotary machine for the large vehicle such as truck and/or bus becomes large necessarily, the necessity of two large electric rotary machines on the vehicle causes the weight of the vehicle to be increased in contradiction to the basic object to improve the fuel efficiency.
In the parallel system, in order to improve the fuel efficiency, a testing of improvement of the utilization efficiency of regenerated energy by improving the efficiency of regenerative braking using the motor-generator as the generator during deceleration of the vehicle has been performed. In the parallel system, however, energy to be obtained by braking is consumed as heat generated by friction of the internal combustion engine, that is, radiated as heat generated by engine-brake, so long as the motor-generator is directly connected to the rotary shaft of the internal combustion engine. Therefore, the regenerated energy can not be effectively utilized as electric energy. In order to avoid this problem, the second clutch is required in the system shown in FIG. 9. In the Volkswagen system mentioned above in which the second clutch is provided between the internal combustion engine and the motor-generator, it is possible, during the regenerative braking, to separate the second clutch such that regenerative braking is not influenced by friction of the internal combustion engine. However, it is necessary, in order to control the second clutch with an appropriate timing, to provide a complicated mechanical device including a large size oil pressure system and an electric mechanism including a number of sensors and program control circuits.
The present invention was made in view of the above mentioned background and has an object to provide a hybrid car having a structure suitable for a large size vehicle and capable of utilizing the merits of both the series system and the parallel system.
Another object of the present invention is to provide a hybrid car, which can generate a large torque by driving an axle of the car with an internal combustion engine and a motor in running along an uphill road or in starting and can substantially improve the fuel efficiency.
Another object of the present invention is to provide a hybrid car, which mounts a single electric rotary machine and is lightweight.
A further object of the present invention is to provide a hybrid car capable of effectively regenerating energy by braking without influence of friction of an internal combustion engine.
Another object of the present invention is to provide a hybrid car having a simplified construction without necessity of providing a second clutch, which is complicated in structure, is heavy and is large in size.
According to the present invention, these objects can be achieved by a hybrid car featured by that an internal combustion engine is connected to a motor-generator not directly but through a unidirectional rotation transmitting means.
That is, the present hybrid car including the internal combustion engine, the motor-generator, a clutch and a change gear, all of which are connected in the sequence such that a rotary driving force is transmitted in the sequence, is featured by that the unidirectional rotation transmitting means, which can transmit a rotary driving force only from the internal combustion engine to the motor-generator, is provided between the internal combustion engine and the motor-generator.
The simplest example of the unidirectional rotation transmitting means may be a rotary ratchet mechanism provided on a rear wheel shaft of a bicycle. The direction of rotation of the internal combustion engine is always constant and is never reversed. The unidirectional rotation transmitting means becomes in a coupling state automatically when the rotation speed of the internal combustion engine becomes higher than that of the motor-generator and becomes in a decoupling or slipping state automatically when the rotation speed of the internal combustion engine becomes lower than that of the motor-generator. In the coupling state, the rotary drive force is transmitted from the internal combustion engine to the motor-generator. When the motor-generator starts to drive the internal combustion engine, the rotation transmitting means becomes the decoupling state, so that the rotary drive force is not transmitted in that direction.
The unidirectional rotation transmitting means may be constructed with any of various known mechanisms based on similar principles to that of the rotary ratchet mechanism. Such mechanisms may be utilized by modifying the designs thereof such that they become suitable for a device for driving large size vehicles.
The present inventors had manufactured and tested a unidirectional clutch as the unidirectional rotation transmitting means. The unidirectional clutch has a structure applicable to a commercial vehicle such as a large size bus and/or large size truck and will be described later.
By utilizing such unidirectional rotation transmitting means, rotation of wheels of a vehicle is transmitted to a motor-generator through a change gear and a clutch when an internal combustion engine becomes an idling state or a low rotation speed state by releasing an accelerator pedal while the vehicle is running at a certain speed. If a braking is performed in this case, it is possible to perform a regenerative braking by operating the motor-generator as a generator. In such case, since a connection between the internal combustion engine and the motor-generator is separated by racing of the unidirectional rotation transmitting means, it is possible to efficiently regenerate mechanical energy generated by the braking by the motor-generator, without any loss of rotation energy due to friction of the internal combustion engine.
When the accelerator pedal is pressed down in a state where the motor-generator operates as the motor by the unidirectional rotation transmitting means and the vehicle is accelerated by electric energy, the rotation speed of the internal combustion engine is increased. Therefore, the unidirectional rotation transmitting means becomes in the coupling state, so that the rotary drive force is transmitted from the internal combustion engine to the drive axle. Therefore, it becomes possible to drive the vehicle by the motor and the internal combustion engine simultaneously to thereby obtain large torque necessary in a short time such as when the vehicle runs an uphill road or starts to run.
When the vehicle makes a backward movement, the unidirectional rotation transmitting means works similarly. That is, since the change gear is in the reverse position when the vehicle is to be moved backward, the motor-generator never rotate in a reverse direction even if the vehicle moves backward. This is different from the case of the ratchet on the bicycle.
The hybrid car according to the present invention comprises control means for controlling the motor-generator and electric storage means connected to the motor-generator through the control means, wherein the control means comprises means for setting any one of the following modes:
(1) a motor running mode in which the motor-generator is operated as the motor to drive the axle through the change gear;
(2) a parallel running mode in which the motor-generator is operated as the motor and the axle is driven by both the motor and the internal combustion engine through the change gear;
(3) an engine running mode in which the motor-generator races and the axle is driven by the internal combustion engine through the change gear;
(4) a running/recharging mode in which the motor-generator is operated as a generator and the axle is driven by the internal combustion engine through the motor-generator and the change gear and, simultaneously, the electric storage means is recharged by electric energy generated by the generator;
(5) a regenerative mode in which the motor-generator is operated as the generator and the generator is driven by the change gear to recharge the electric storage means by electric energy generated by the generator; and
(6) a parking/recharging mode in which the motor-generator is operated as the generator and the generator is driven by the internal combustion engine to recharge the electric storage means by electric energy generated by the generator.
Further, the motor-generator of the hybrid car according to the present invention is preferably a synchronous rotary machine including a permanent magnet. In such case, the control means may include a bidirectional inverter for converting a multi-phase A.C. output of the synchronous rotary machine into a D.C. current and supplying the D.C. current to the electric storage means and for converting an output D.C. current of the electric storage means into a multi-phase A.C. output and supplying the multi-phase A.C. output to the synchronous rotary machine, a first rotation sensor for detecting rotation of the motor-generator, a second rotation sensor for detecting rotation of the internal combustion engine and a program control circuit responsive to outputs of these two rotation sensors for monitoring an operation of the unidirectional rotation transmitting means and controlling the A.C. frequency of the inverter.
The hybrid car according to the present invention may have a construction in which a residual capacity of the electric storage means is monitored and taken in the control means to select and set an appropriate operation mode. When the electric storage means is a large capacitor, it is possible to monitor the residual capacity by monitoring a terminal voltage thereof. When the electric storage means is a chemical storage battery having a simple construction, it may be preferable to estimate the residual capacity by utilizing a terminal voltage thereof Techniques for monitoring the residual capacity of the electric storage means in more detail by monitoring temperature and/or specific gravity of solution have been known and can be utilized.
For using a unidirectional clutch as the unidirectional rotation transmitting means, it is preferable to arrange a unidirectional clutch in an inside space of a rotor of a motor-generator. The basic structure and operation of the unidirectional clutch are the same as those of a rotary ratchet mechanism mounted on a rear wheel of a bicycle and includes an outer ring, an inner ring and sprags for coupling the outer and inner rings. The outer ring is connected to a crank shaft of an internal combustion engine and the inner ring is coupled in the inside space of the rotor of the motor-generator.
That is, the unidirectional clutch is disposed in a space provided in inside of a rotor of the motor-generator and a stator of the motor-generator is disposed in an outer peripheral space of the rotor. With this structure, length of the rotary shaft measured from the crank shaft of the internal combustion up to the change gear is not increased substantially by the provision of the unidirectional clutch.